texts: Position and velocity vectors of nearby stars?

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One of my favorite tools for modeling the solar system is the Horizons Ephemeris generator where I can get position and velocity vectors of various bodies. Is there something similar for neighboring stars?

The closest I've come so far is Ashland Studio's 500 nearest stars in the Hipparcos Catalog. It gives distance of each star. Clicking on a star in this list will often give the star's relative velocity wrt our solar system. But it doesn't the direction of it's motion.

For the time being I'd like the model the stars within about 20 lightyears of Sol.


texts: How does gyrochronology deal with differential rotation and axial tilt?

texts: K2 seems to become an even better mission than what a continuation of Kepler would have been, at least to some astronomers. By what means is differential star rotation being dealt with? The rotational period of the Sun is 45% longer at its poles than at its equator. Together with the unknown orientation of the star's rotational axis, can this really be sorted out from Doppler broadening of spectral lines? Is a star's rotational period defined as that of its equator or as some average across its surface?


texts: An hypothetical timepiece on board of a spaceship. Please Help

texts: On board of a hypothetical spaceship, I have a hypothetical clock consisting of 2 mirrors and a light beam is being reflected between the mirrors to measure the time. Now if we hypothetically exceed the speed of light; what will I see is happening to my clock on board of my ship? (a) Light can't exceed the speed of light so according to me the clock has freezed, (b) Light always passes the observer at the speed of light, so my clock is keeping perfectly time but the speed of light inside my clock has surpassed the speed of light? (c) The clock will run backwards?  I just can't wrap my mind around this problem.


texts: Estimating inner and outer boundaries of habitable zone for Sun

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What would the inner and outer boundaries of the “habitable zone” be for planets with an albedo that differs from that of the Earth?

For example a planet with an albedo of 0.07 or 0.90 (the values for Mercury and Venus, respectively).

I want to compare these values to the distances in AU's of the rocky inner planets.


texts: Why do not we use optical telescopes to study cosmic rays directly?

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HESS, CTA, and VERITAS are used to study cosmic rays.

What they receive are optical (maybe very blue) photons.
So my question is: Why don't we use optical telescopes to study cosmic rays directly?


texts: Is it possible for a moon to orbit a planet floating free in the galaxy rather than orbiting a star

texts: This article got me thinking, can a planet hold a moon in orbit if it is just floating in the galaxy by itself not as part of a star system? Can a celestial body even qualify as a planet if it is floating around by itself?


texts: What happens if one day aliens want to talk to us. How can we talk to them?

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Always I wonder about that if some day alien wants to talk to us, then how can we talk to them? They didn't know any of the language on the Earth.

What will be the basic building blocks for it?


texts: I’m in New Zealand and have just seen two lines of uniform stars in parallel lines moving slowly from east and disappearing into nothing right above us. They went on for nearly two minutes before the last one vanished and were not like the star link satellites that move in one tight line from horizon to horizon, they were more spaced out and coming from far off and disappearing into somewhere above us. Also it looked like a shooting star came out of the line and one of the stars was them missing from the uniform lines. Any ideas? Thanks


texts: What is the predominant element in the dust of the Sombrero Galaxy?

texts: The Sombrero Galaxy contains a rather peculiar ring of dust orbiting it (seen as the dark ring on the outer edge). What is the prevalent element in this dust? Carbon?


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The title basically says it all. As seen from the Earth, is it possible for the Moon to eclipse Venus (or any other planet) or are the orbits inclined such that this never happens?

If such an eclipse is possible, is it a frequent or infrequent event? How would I find out when the next one occurs?


texts: How far are we from the edge of the Universe?

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Following the Big Bang the Universe continues to expand, presumably and roughly equally in all directions. It is understood that the Big Bang occurred 13.798 ± 0.037 billion years ago.

Is there any way for us to know how far we are away from the nearest edge of the expansion front of the Big Bang?


texts: Shooting stars are actually meteors falling down on the surface of earth. How come some of them appear shooting up and not down?


texts: Is there an antonym for 'transit', i.e. the transit of a celestial body through the meridian

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I'm writing software to calculate the rising, transit, and setting of a body on the celestial sphere for a specific location and date. It seems to me that the opposite of transit, at least in the case of the Sun and for circumpolar stars, would also be of importance.
In the northern hemisphere this would be the time when a circumpolar star would pass through the line between the celestial north pole and true north, and be at its lowest height above the horizon.
Is there an antonym (opposite) for the word transit?


texts: Forms of stellar orbits around the galactic center

texts: Do all stars in orbit around Sagittarius A have approximately circular orbits or are there stars that orbit the Milky Way center very elliptically, like being in the Milky Way's outer rim at apoapsis and in the core worlds close to Sagittarius A at periapsis? Do we know what orbital eccentricity the Sun (respectively the Sun-Jupiter barycenter) has?


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I'm trying to write a Python program that will do the following: take an image in fits format and a reg file with a list of regions in the sky, and determine which regions in the list are inside the fits image and which ones are outside. This can be done visually with ds9, but I have no idea of how I can access the fits file and determine the coordinates of the boundary of the image.

Any advice? I don't know much about the fits format, but it won't open with a usual text editor like gedit.

Edit: Now I have a more specific problem. I have four points in the sky defined by their declination and right ascension. Is there a simple way to check if these coordinates belong to the image coded in the fits file?

Edit 2: This is what I see as the header of my fits file:

I'm no expert in physics, just a mathematician, so I'm not sure how to proceed from here. Any help would be appreciated...

Edit 3: Something seems to change when I put the terminal in full screen mode. Is there any useful info here?


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There is a large number of visible Supernovas. Each week - about a 20 Supernovas Type 1a around the Universe.

Is there collisions of Black Holes? What is this collision called?

E.g. 2 black holes come close to each other. There are event horizons for both black holes, will this made such collision super long in Earth's time?


texts: Measuring misalignment between two positions on sky

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Let's say I have the (RA,Dec) for two positions on the sky. I want to measure the position angle between these two positions. In other words, if I had the Cartesian coordinate vectors for these two positions (say [x,y,z]) then I think the position angle PA would simply be the dot product of the two vectors, so basically cos(PA). However, RA and Dec are spherical coordinates (corresponding to $\phi$ and $\theta$ respectively), not Cartesian coordinates. How do I get cos(PA) between the two positions on the sky if I only have their (RA,Dec) instead of [x,y,z]?

https://en.wikipedia.org/wiki/Position_angle

  Position angle, usually abbreviated PA, is [a] convention for measuring angles on the sky in astronomy. The International Astronomical Union defines it as the angle measured relative to the north celestial pole (NCP), turning positive into the direction of the right ascension. In the standard (non-flipped) images this is a counterclockwise measure relative to the axis into the direction of positive declination.


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What events could have to happen to Mars (which is thought to once look like Earth) that may have depleted the atmosphere and erase all proof of life ever existing at least on the surface?

I know an asteroid could melt the planet but could there have been an event that could wipe the surface while leaving deposits under the ground intact?

There is no proof that Mars melted but there is proof that there at least was oceans.

http://en.yibada.com/articles/18182/20150309/red-planet-once-held-large-shallow-ocean-mean-positive-signs.htm

Where did Mars water go?


texts: angle to the equator of the Sun on sky at a given time

texts: Is there an easy way to tell at what angle the solar equator is wrt the horizon at any given time of the day? I would think that it rotates 180 degrees from sunrise to sunset, but not in a linear fashion. But solar noon should always be 0 degrees wrt the horizon right?


texts: Why do stars rotate slower than they're expected to?

texts: Due to conservation of angular momentum, I thought most stars would be spinning extremely fast because they have a relatively small diameter. However, it turns out that this is not true and most stars actually spin "slow"? Why is this the case?


texts: Why the Circumstellar Habitable Zone is defined as it is, if life could be possible outside of it?

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According to Circumstellar habitable zone

  In astronomy and astrobiology, the circumstellar habitable zone (CHZ), or simply the habitable zone, is the range of orbits around a star within which a planetary surface can support liquid water given sufficient atmospheric pressure

But then you have moons in the solar system such as Titan, Europe, Enceladus where some scientists believe life could be possible.

The most likely cradles for life inside our solar system

Life on Titan

Why the CHZ is defined as it is, if life could be possible outside of it? Is it pourly defined or scientists believing there could be life outside the CHZ in the solar system are having too much wishful thinking?


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According to this website, Bond albedos are computed by calculating the ratio of the flux reflected by a planet (integrated over wavelength) to the total stellar flux incident on the planet.
Three questions:

How to arrive to "the ratio of the flux reflected by" the earth?
How to arrive to "the total stellar flux incident on" the earth?
How to compute the two together?


texts: Why Milky Way and Andromeda are being drawn together if there was 'Big Bang'?

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Scientists used to use following reasoning:

most galaxies are red-shifted $\implies$ there was a 'Big Bang'

Why this is being considered valid since not every galaxy has such property?


texts: Why does the Sun deviate from a typical blackbody spectrum in the S band?

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This is sort of a follow-up to this question, and my answer to it.
The graph I see here details the radio (and other frequencies) emission of the sun. What's most notable and interesting to me is the deviation from the typical blackbody spectrum of a body at around 6000 K. The sun seems much brighter in the S band (and at some larger wavelengths) than a typical blackbody.
My question is: why does this happen? Is there an underlying physical/astrophysical phenomena that we know of that causes this? Or is this something that's undergoing research right now?


texts: What is the maximum transmission distance of the radio signal in the outer space which could still be understood?

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I’ll put this question in a form of a physics problem:
Transmitter at a point A sends a signal to a receiver at a point B. What is the longest distance in light years from points A to B for which receiver can still understand the signal?

Given:

Signal type: electromagnetic wave.
Signal frequency: frequency for which signal fades the least - probably radio.
Signal form:

Variant 1: beam of highest concentration possible.
Variant 2: full sphere.

Transmitter power: power of the most powerful transmitter known to be built in the Earth.
Receiver: sensitivity of the most sensitive receiver known to be built in the Earth.
Transmission medium: interstellar space.
Understanding of a signal:

Variant A: Can detect that the signal is not a noise.
Variant B: Can decode the information in the signal.


texts: Why aren't GPS clocks sufficient to synchronize VLBI observations?

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In very long baseline interferometry, it is typical to use a hydrogen maser atomic clock to sample data. However, given how expensive these atomic clocks are, it seems surprising that more observatories aren't using non-local atomic clocks, such as GPS clocks.

This Wikipedia article says "The antenna signal is sampled with an extremely precise and stable atomic clock (usually a hydrogen maser) that is additionally locked onto a GPS time standard." My question is, why not do away with the hydrogen maser entirely?


texts: Could a near collision with small black hole account for the effects of the 9th planet?

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Much interest has been raised about the existence of a 9th planet. One reason for this is the strange orbits of bodies in the outer solar system. Could the orbits be explained by a near collision of a passing black hole?
Recent work is looking to see if the 9th planet could be a small black hole. But my question is different. Could a passing black hole, say a million years ago, have thrown the objects in the outer solar system into the strange orbits they exhibit?


texts: How far away is the light that would reveal the Big Bang?

texts: I guess theoretically if we could go faster than light, which we clearly cannot, at some point we'd be able to see the big bang itself. Just curious - how far away is that light?


texts: How do stars affect the orbits of moons?

texts: I asked a question previous similar to this, but I'm wondering, can a star make a moon move closer to its planet or further away? How?


texts: How can a mirror see things that the naked eye can’t?

texts: How does a mirror pick up light from vast distances away? And, if that light can reach a mirror, why can’t we see that light?


texts: Can a donut-shape planet or star be formed?

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How stable is a donut-shaped star or planet configuration and under what conditions such object may form?
Is there any evidence suggesting that such objects might exist?


texts: September 26 twelve hours sunrise to sunset?

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I noticed in today's newspaper (Boston Globe, September 26) that sunrise and sunset were both at 6:25. That's the twelve hour day I'd have expected at the equinox.

(Please retag if there's a better one)


texts: IAU Dwarf planet definition Point 2.b - is not a satellite

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I am a bit confused with point 2.d of the IAU's resolution on dwarf planets.

(2) A "dwarf planet" is a celestial body that
(a) is in orbit around the Sun
(b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape
(c) has not cleared the neighbourhood around its orbit
(d) is not a satellite.

http://www.iau.org/static/resolutions/Resolution_GA26-5-6.pdf
I notice that a lot of websites exclude this point all together? Some of
them even rather combine it with point 2.a ? Like over here
Feels a bit redundant, since orbits the sun implies not orbiting a planet?
Or am I missing something here?


texts: Do black holes pull in and keep spacetime itself or merely warp it but ultimately let it pass through?

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Forgive my 'amazing' MS-Paint skills, but this is along the lines of what i'm wondering:

Is there any situation where Scenario A occurs, or is space always dragged back out as in Scenario B?


texts:
The Wikipedia article on photometry says that

  These have largely been replaced with CCD cameras that can simultaneously image multiple objects, although photoelectric photometers are still used in special situations, such as where fine time resolution is required.

How much the research community is using photometers today? I looked up the prices of some photometers from here. The device, filters, etc. can cost nearly $2500. One could get a good CCD camera with that price.

What are some applications where the good time resolution (apparently around 1 ms) would be needed? Are photometers equally useful with small telescopes (e.g. 8-inch) as CCDs?


texts: Earth's magnetic field vs. refrigerator magnet

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According to this article:

  The Earth's field ranges between approximately 25,000 and 65,000 nT
  (0.25–0.65 G). By comparison, a strong refrigerator magnet has a field
  of about 10,000,000 nanoteslas (100 G)

The Earth's magnetic field is between 150 and 400 times weaker than a refrigerator magnet.

Question: Can any magnet (or even one much stronger) of the Earth divert the cosmic rays as Earth's? Do these magnets somehow "interfere" with Earth's? If not, Why? Maybe because the size (not the power)?


texts: How far away are objects whose light will never reach us, because of the expansion of the universe?

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I thought I had read this question on Stack Exchange before, but now I cannot find it...   In fact, I thought I had posted this question before, somewhere, on Stack Exchange...
I believe the answer was about 62 billion light years...
In other words, if an object is currently 62 billion light years away, or more, the light it is emitting right now will never reach Earth...
Is there a term for this 'line' or 'sphere'?


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Since space is mostly empty, one might first think that the majority of the photons, e.g. emissions from the stars since the beginning of the universe, are still in flight and not absorbed by anything.

Is this true?

Is there any estimates that the proportion is relative to the total amount of photons ever created?

(Let's consider the photons that have made it into space first, e.g. exclude the photons that gets absorbed and re-emitted inside stars for now).


texts: Units of integrated flux density (irradiance) along longitudes

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If I've taken an image of the Galactic bulge with the pixel units in MJ per steradian:

and I've looked down each column of the image and added up the values:

then do the units change? My thinking is that I'm taking something that is measured per steradian (which is a solid angle) and integrated it along a single axis, which would be in degrees. Would this make the units of my graph now MJ per radian? Or am I simply adding values in MJ per sr, so the units don't change?


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I have heard a certain statement, which can be summarized succinctly into "we live in a local bubble", implying that solar system is located in an intestrellar dust underdensity region.

This region is allegedly produced by a supernova explosion, which happened near the Sun in the distant past. The bubble size was claimed to be of order of few tens of parsec, and the fact of its existence allows one to easier deal with dust extinction for nearby stars.

Another claim I have heard about this bubble, is that this concept is obsolete nowadays, for if even if there were a supernova taking place near the Sun, gas diffusion timescales are short enough, so that no vestige would have remained from this past event by now.

I would like to ask you, therefore, to comment on the text above and in particular indicate, whether such an underdensity really exists, and what do we know about it.


texts: Is there any synthetic spectrum software for neutron star?

texts: Is there any software that can calculate the emergent spectrum of a neutron star photosphere, for Teff is about 1e7K, density is above 1e21-1e22 cm^-3 ? Output line wavelength is about 0-100A is enough. Can calculate Fe and heavier metal isotope like Ni. Since the dense and temperature is high, many softwares seem do not suitable.


texts: Simple mathematical models of solar systems

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I’m a hobbyist programmer with a profound love for procedural content generation.  I’m working on a 2D space exploration game and while it’s not meant to simulate anything real, I’d like to give it a natural feel.  I have no real knowledge in astronomy, so I figured someone here should have an answer.

I was wondering if there are a few simple mathematical models I could use to determine some parameters for my generation algorithm.

the orbital radius of the planets
the size of the planets (is it more likely that gas giants and the likes will show up closer to the sun or further away, etc.)
the number of planets orbiting a star

Also, a few questions come to my mind too:

is it a common occurence to have a star with nothing orbiting it?  Like just a single lone star sitting there in the middle of space.
IIRC, Earth is kind of a weird thing (besides the fact that it hosts life) because our moon is way bigger than the average moons and also the only satellite of the planet.  Is there any usual correllation between the planet size/density and the size or number of moons around it?
Is an asteroid belt something common in solar systems?

Thanks a lot for your help!


texts: If we had the right technology could we see a distant star in detail?

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If, for instance, Hubble's camera was a $10^{300}$ times better, could it see a distant star in details, or is there a limit to the amount of light that reaches the Earth's orbit or perhaps does the light get distorted on its way so you must come closer?
Is there a limit to the number of light beams that hit a telescope camera's "eye" or if you built a huge telescope would you then be able to see that distant star in high detail (for instance, see an earth size satellite around Betelgeuse's orbit).


texts: If I had a horseshoe orbit of two moons...

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Consider an Earth-like planet, with two moons. I guess the two moons would have to be smaller than our own, for the system to be stable. Is that stable? I did some research, and apparently Janus and Epimetheus (Saturn moons that are in a horseshoe orbit) are like that, but I don't know how their cycles work, or how they look from Saturn.

Hence,:

Would a moon have to be smaller that the other one, or would both have to be the same size?
Would both have the same cycle?
How could nights be seen from the Earth?

I'm looking for that sort of answer.
Thanks in advance! :)


texts: When will the next summer solstice and a full moon coincide? What day?

texts: What day will the summer solstice and full moon coincide? As far as I know the next time will be in 2016. I would like to know what day.


texts: Black hole at Galactic Center of the Milky way and Bar of stars?

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The Milky Way is a barred spiral galaxy, with a supermassive black hole at its center. Here

As it is a barred spiral galaxy, it has a central bar-shaped structure composed of stars.Here

So my questions are -:

Do the bar and supermassive black hole overlap or cross each other?
Do the stars from the bar get sucked inside the supermassive black hole?